The enormous growth in network communications has been due in part to software applications' increased abilities to interact with each other across Wide Area Networks (“WANs”). The transmission of large amounts of data across WANs, however, creates special challenges for achieving a high degree of application and network performance. To fully appreciate the extent of these challenges, a brief primer on basic network concepts will now be provided for background purposes, beginning with a discussion on the Open Systems Interconnection (“OSI”) conceptual network model.
The OSI model is commonly used to define the flow of data, or “network traffic,” over a network between network applications and/or devices. The OSI model has seven layers including the application layer (“Layer-7”), the presentation layer (“Layer-6”), the session layer (“Layer-5”), the transport layer (“Layer-4”), the network layer (“Layer-3”), the data link layer (“Layer-2”), and the physical layer (“Layer-1”). Each OSI layer communicates with a layer above and/or below it and with corresponding layer(s) on other applications and/or devices in the network through specific protocols. The network layers are often referred to as “the network stack,” and the most common protocols in which these layers are implemented are the TCP/IP protocols.
The TCP portion of the protocol corresponds to the Layer-4 transport layer in the OSI model. The IP portion of the protocol defines standards for data packets that may comprise data message(s) at the Layer-7 application layer. The TCP/IP protocols ensure the reliable, in order delivery of data. For instance, an application on a first device (e.g., client) may request that data be sent to another application at a second device (e.g., server).
The client's TCP/IP stack, typically implemented in the operating system kernel, may eventually partition the data into Layer-7 application layer messages to be transmitted over a Layer-1 physical connection. The data transmitted is typically acknowledged as it is received in a specified order, and lack of an acknowledgement from its intended recipient often results in portions of the data being resent. When portions of data are received out of sequence, however, the TCP/IP regime nevertheless requires waiting for the remaining portions of data before any processing can be performed by the recipient upon the data, a condition known as “head of line blocking.”
The growing complexity and sophistication of more elegant network application solutions recently, however, have been increasingly frustrated by the rigidity of the TCP/IP approach. For instance, while the TCP/IP protocols ensure the reliable, in order delivery of data, they do not recognize acceptable exceptions for violating the in order delivery of data maxim. As network applications become ever more sophisticated, the ability to send data out of order may help overcome TCP/IP's limitations and sustain their continued growth.